import java.util.LinkedList;
import java.util.Queue;
import java.util.Stack;

public class BinaryTree {

    static class TreeNode {
        public char val;
        public TreeNode left;//左孩子的引用
        public TreeNode right;//右孩子的引用

        public TreeNode(char val) {
            this.val = val;
        }
    }


    /**
     * 创建一棵二叉树 返回这棵树的根节点
     *
     * @return
     */
    public TreeNode createTree() {
        TreeNode A=new TreeNode('a');
        TreeNode B=new TreeNode('b');
        TreeNode C=new TreeNode('c');
        TreeNode D=new TreeNode('d');
        TreeNode E=new TreeNode('e');
        A.left=B;
        A.right=C;
        B.left=D;
        B.right=E;
        return A;
    }

    // 前序遍历
    public void preOrder(TreeNode root) {
        if(root==null){
            return;
        }
        System.out.print(root.val+" ");
        preOrder(root.left);
        preOrder(root.right);
    }

    // 中序遍历
    void inOrder(TreeNode root) {
        if(root==null){
            return;
        }
        inOrder(root.left);
        System.out.print(root.val+" ");
        inOrder(root.right);
    }

    // 后序遍历
    void postOrder(TreeNode root) {
        if(root==null){
            return;
        }
        postOrder(root.left);
        postOrder(root.right);
        System.out.print(root.val+" ");
    }

    public static int nodeSize;

    /**
     * 获取树中节点的个数：遍历思路
     */
    void size(TreeNode root) {
        if(root==null){
            return;
        }
        nodeSize++;
        size(root.left);
        size(root.right);
    }

    /**
     * 获取节点的个数：子问题的思路
     *
     * @param root
     * @return
     */
    int size2(TreeNode root) {
        if(root==null){
            return 0;
        }
        return size2(root.left)+size2(root.right)+1;
    }


    /*
     获取叶子节点的个数：遍历思路
     */
    public static int leafSize = 0;

    void getLeafNodeCount1(TreeNode root) {
        if(root==null){
            return;
        }
        if(root.left==null&&root.right==null){
            leafSize++;
        }
        getLeafNodeCount1(root.left);
        getLeafNodeCount1(root.right);
    }

    /*
     获取叶子节点的个数：子问题
     */
    int getLeafNodeCount2(TreeNode root) {
        if(root==null){
            return 0;
        }
        if(root.left==null&&root.right==null){
            return 1;
        }
        return getLeafNodeCount2(root.left)+getLeafNodeCount2(root.right);
    }

    /*
    获取第K层节点的个数
     */
    int getKLevelNodeCount(TreeNode root, int k) {
        if(root==null){
            return 0;
        }
        if(k==1){
            return 1;
        }

        return getKLevelNodeCount(root.left,k-1)+getKLevelNodeCount(root.right,k-1);
    }

    /*
     获取二叉树的高度
     时间复杂度：O(N)
     */
    int getHeight(TreeNode root) {
        if(root==null){
            return 0;
        }
        int left=getHeight(root.left);
        int right=getHeight(root.right);
        return left>right? left+1:right+1;
    }


    // 检测值为value的元素是否存在
    TreeNode find(TreeNode root, char val) {
        if(root==null){
            return null;
        }
        if(root.val==val){
            return root;
        }

        TreeNode findLeft=find(root.left,val);
        if(findLeft!=null){
            return findLeft;
        }
        TreeNode findRight=find(root.right,val);
        if(findRight!=null){
            return findRight;
        }
        return null;
    }

    //层序遍历
    void levelOrder(TreeNode root) {
        if(root==null){
            return;
        }

        Queue<TreeNode> qu=new LinkedList<>();
        qu.offer(root);
        while(!qu.isEmpty()){
            TreeNode cur=qu.poll();
            System.out.print(cur.val+" ");
            if(cur.left!=null){
                qu.offer(cur.left);
            }
            if(cur.right!=null){
                qu.offer(cur.right);
            }
        }
    }


    // 判断一棵树是不是完全二叉树
    boolean isCompleteTree(TreeNode root) {
        if(root == null){
            return true;
        }
        Queue<TreeNode> qu=new LinkedList<>();
        qu.offer(root);
        while(!qu.isEmpty()){
            TreeNode cur=qu.poll();
            if(cur!=null){
                qu.offer(cur.left);
                qu.offer(cur.right);
            }else {
                break;
            }
        }
        while (!qu.isEmpty()){
            TreeNode peek=qu.peek();
            if(peek!=null){
                return false;
            }
            qu.poll();
        }
        return true;
    }
    public void postOrderNor(TreeNode root){
        if(root==null){
            return;
        }
        Stack<TreeNode> stack = new Stack<>();
        TreeNode cur=root;
        TreeNode prev=null;
        while(cur!=null||!stack.isEmpty()){
            while (cur!=null){
                stack.push(cur);
                cur=cur.left;
            }
            TreeNode top=stack.peek();
            if(top.right==null||top.right==prev){
                System.out.print(top.val+" ");
                stack.pop();
                prev=top;
            }else {
                cur=top.right;
            }
        }
    }
}
